Photodetectors having light detecting elements that detect light are known. Technologies for increasing the thickness of depletion layers and technologies for forming irregularities in at least areas of a silicon substrate opposed to p-n junctions have been disclosed as technologies for increasing sensitivity of a photodetector to light in the near-infrared range.
When the thickness of depletion layers is increased, drive voltage needs to be made higher. Furthermore, when the thickness of depletion layers is increased, array miniaturization of light detection elements becomes difficult. Furthermore, a dedicated processing apparatus is necessary for forming irregularities on a silicon substrate. Thus, in related art, it is difficult to improve the sensitivity to light in the near-infrared range with a simple structure.